Introduction

1. 1,3-Butadiene is a chemical compound, the molecule of which comprises four carbon and six hydrogen atoms. At normal ambient temperatures it is a gas, and trace amounts can be found in the atmosphere that we breathe. These derive mainly from the combustion of petroleum in motor vehicle engines and from other sources of combustion such as fossil fuels and accidental fires.
2. 1,3-Butadiene is used in industry, mainly in the production of synthetic rubber for tyres. It is also present in a number of commercial liquid petroleum gases. It is thus a chemical to which workers have been exposed, and there is evidence that such groups of workers have had a slightly higher than expected risk of cancers of the lymphoid system and bone marrow, lymphomas and leukaemias. Laboratory studies have shown that 1,3-butadiene causes a variety of cancers in rodents and damages the genetic structures of the cell. It is thus a genotoxic carcinogen and, in theory, it is not possible to determine an absolutely safe level for human exposure.
3. In practice, however, it is clear from studies of groups of workers, many of whom have had substantial exposure to 1,3-butadiene, that risks to the general population from the levels currently found in the atmosphere in the United Kingdom must be exceedingly small. We nevertheless recommend that steps should be taken to keep levels as low as is practicable. In this document we summarise briefly the main sources, methods of measurement and evidence of health risks of 1,3-butadiene. We then recommend an Air Quality Standard for the United Kingdom, based on the best evidence available.